This invention relates to automatic testing equipment (ATE) for electronic circuits and, more particularly, to an improved architecture and receiver for interfacing the ATE to a device under test.
Electronic circuit boards are often tested to find and remove defects before the boards are sold to end users. The tests often consist of simulating the intended operating environment of the circuit board and comparing the output from the circuit board to the output expected from a defect-free board. The test input may be a sine wave, a ramped voltage input or a current pulse applied to the board inputs. The test inputs also may be similar voltages or currents applied to specific nodes within the circuit.
To accomplish the foregoing, the typical ATE must include (1) a mechanism for transmitting the input to the circuit board being tested; and (2) a mechanism for receiving the test results from the circuit board. The ATE element that performs these functions is called the receiver. The receiver is ordinarily coupled to a driver/sensor board which functions as a voltage and current source capable of generating a variety of analog and digital input signals, such as sine waves, square waves and the like. The driver/sensor board generates test signals, then relays test signal responses to a central processing unit. Multiple driver/sensor boards are mounted to a common backplane allowing communication among the driver/sensor boards and to and from a central processing unit or control workstation.
To test a circuit board on known ATE's, the circuit board is mounted on a fixture which has I/O pins that make electrical contact with either the regular circuit board input pins or with specific nodes within the circuit. Vacuum is typically used to secure the circuit board to the fixture. The fixture has other I/O pins that mate with corresponding I/O pins on the receiver. The correspondence between the input and output pins of the fixture is governed by the fixture's internal wiring.
Known ATE's include a fixed I/O pin mapping to the underside of the fixture using cables. Thus, although different fixtures can be substituted for testing different circuit board layouts, the underside of any fixture to be connected to a given ATE has the same layout. Accordingly, known ATE's are not adaptable for use with different fixture undersides.
Further, known ATE's have many problems associated with them. For example, the use of a common backplane for all pin cards limit the variety of tests that can be executed by a single ATE. Furthermore, extensive wire cabling often is used to connect the driver/sensor board with the receiver I/O pins and to connect the fixture I/O pins with the receiver. This can create undesirable noise interference as the current variations in each wire induce voltages in adjacent wires. As a result, the quality of the generated test signals and the resulting output signals may deteriorate significantly before reaching their respective destinations. The effect of the noise is particularly severe at high frequencies.
In addition, lengthy ground wires often are used for grounding conventional ATE system elements. The effectiveness of the grounding of each ATE element diminishes as the length of the ground wire increases. For example, each receiver pin card, as well as a circuit board under test, is grounded by connection to a ground source at a driver/sensor board base. Such a lengthy ground wire connection contributes to variations in the signals generated by the individual pin cards and hence affects the accuracy of the test results.